There are many situations in which electrical signals must be communicated between two devices that are moving with respect to one another. This is typically accomplished by electrically connecting the devices using a communication cable, usually called a patch cord. Because the patch cord is normally exposed to flexing in various modes, and often at a very high frequency, the patch cords frequently fail in various ways. These failure modes can result in short circuits, loss of signal, or deterioration of signal.
What is needed is a light weight and cost effective, high flex, Ethernet type data cable that has dual shields for high shielding effectiveness. Paramount to a successful design will be the cable's ability to endure repetitive and continuous flexing through an unsupported bend radius. Testing will entail a sequence of 1 million flex cycles at 10× cable diameter and 10 million flex cycles at 20× cable diameter in a rolling bend without the benefit of a “C-Track” or mandrels to support the cable along it's length. A viable product will survive the flex test battery without visible physical damage and more importantly, will retain the original level of shielding effectiveness while also meeting or exceeding the industry accepted TIA 568B requirements for a Cat 5e, Cat. 6 and Cat 6a product.
Typical cable that is not intended for high flex applications will have a polyester tape around the core followed by a laminated foil tape and then the braid. In order to reduce signal loss and improve shielding effectiveness the laminated tape will usually be 0.002″ or more thick. Unfortunately, the thicker the tape the more apt it is to crack. Once the internal tape on a traditional cable cracks, it produces sharp edges that will ‘saw’ on the core insulation during movement until it eventually causes cable shorting and/or failure. In some cases the shielding tape does not crack immediately, but will crease and fold. This folding will cause bending stress to be concentrated. That is the bend radius of the cable will actually become smaller where the foil is creased. This causes the wires in the core to exceed their bend radius limits and quickly fail. Where the bending stress is concentrated, the shield tape will often fail with a 360 degree crack which will reduce the shielding effectiveness. This interruption in the shield tape leads to lower conductivity (higher shield resistance) over the entire length of the cable. The braid applied to traditional cables is normally applied with a 20 to 40 degree angle. This construction will typically not perform well after a relatively low number of flex cycles because it doesn't allow the range of movement for the braid strands that the higher 45 degree angle braid of the cable of this invention provides.
In current high flex designs the foil is eliminated. Often a barrier layer of extruded material or a tape is applied over the core to prevent insulation abrasion by the braid movement. This construction eliminates the failures due to the tape however the cable will have lower shielding effectiveness at some frequencies when compared with a cable with a shield tape applied. One way to improve the shielding effectiveness is to manufacture a double shielded cable with two thick braids and no foil tape. This method results in a cable that is heavy and expensive.
These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.
It is, therefore, an outstanding object of some embodiments of the present invention to provide a communication cable that is resistant to deterioration or failure caused by flexing.
It is a further object of some embodiments of the invention to provide a communication cable that is capable of being manufactured of high quality and at a low cost, enjoys minimum installation costs, provides highly effective function, and which is capable of providing a long and useful life with a minimum of maintenance.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto, it being understood that changes in the precise embodiment of the invention herein disclosed may be made within the scope of what is claimed without departing from the spirit of the invention.